[rbridge] Proposed resolution of DRB election/MTU testing

[Radia Perlman]

Les Ginsberg (ginsberg) wrote:
>
>   
>> R1.17 is the LAN ID (aka "pseudonode ID"),
>> R3 has no way of whether R1 should be higher priority or not.
>>     
>
> R3 would know this from the hellos it receives from R1.17.
> Or are you suggesting that R3 should take R2's word for it and override
> it's own internal logic as to who should be DRB even if it had not heard
> from R1? 
> (I certainly hope not...)
>
>   
R3 would not necessarily hear R1's TRILL-Hellos, so this is for the case
where R3 can hear R2 and R1, but R3 can't hear R1.
So yes, I was saying that we could have R2 tell R3 about R1.
I didn't put that into the original proposal -- it's an additional 
safety mechanism, and what I hinted
about when I said "R3 defers to any RBridge with higher ID and priority 
that R3 hears from or about".

I don't feel strongly about this. There's trivial overhead to including 
the field in the TRILL-Hello.
>
> The system ID is required to have exactly those properties i.e. it is
> required to be unique area wide at Level 1 and unique domain wide at
> Level 2. This is obviously necessary so as not to confuse the LSPs
> generated by two different systems.
>
>    Les
>
>   
Of course the system ID has to be consistent and unique. I was talking 
about the LAN ID.
There's no reason why R1 couldn't name a pseudonode any 7 byte quantity 
that had
nonzero 7th byte, and top 6 bytes guaranteed not to be used by anyone 
else. So for instance,
if R1 had MAC addresses R1a, R1b, R1c, ... on each of its links, and 
chose R1a as its
system ID, there wasn't anything in the design of DECnet/IS-IS that 
depended on R1 choosing
all its LAN ID's with top 6 bytes = R1a. Given that R1 "owns" MAC 
addresses R1b and R1c as well,
it certainly could give LAN IDs of R1b.15 to one of its links, and 
R1c.12 to another,
and R1a.15 to a third. Just so long as the 7 byte quantity is guaranteed 
unique within the campus.

I was curious since several people have told me over the years (since 
DECnet)
that the top 6 bytes *have to*
be the system ID of the DR. I was wondering where that requirement came 
from, and whether it's just folklore, or whether
there is now anything in IS-IS that would break if the top 6 bytes of a 
LAN ID were not
equal to the system ID of the DR?

Note that this question really doesn't have much to do with closing on 
the details of the proposal in this thread...I just
am curious.

Radia